The discussion below is merely provided for general background information and is not intended to be used as an aid in determining the scope of the claimed subject matter.
Radio-frequency identification (RFID) is a wireless technique, which uses radio-frequency electromagnetic (EM) fields to transfer data for the purposes of automatically identifying and tracking tags attached to objects. A battery-less tag, usually referred to as passive tag, has no power source of its own but collects energy from an interrogating EM field originating from a detection antenna of an RFID reader. The tag acts as a passive transponder emitting microwaves or ultra-high frequency (UHF) signals to the detection antenna. Passive tags are relatively inexpensive to manufacture and can be used as disposable tags.
One problem relates to the fact that, when used in sports timing applications, the UHF tag is within close proximity of the body, which has a dielectric of relatively high dielectric constant. The proximity of the body changes the impedance of the tag antenna thereby “detuning” the tag away from its optimum working point. Due to this detuning effect, the modulated backscatter signal that is generated by the tag will be very small and thus very hard to detect. The detuning is even worse in a wet environment, e.g. wet and sweaty clothing and/or body of an athlete. This way, the signal may further deteriorate thereby increasing the risk that a participant crossing or passing a detection antenna is not or at least not correctly registered by the timing system.
Another problem relates to movement of an UHF sports timing tag relative to the detection antenna when an athlete passes the finish. Due to the movement and/or rotation during the finish crossing, it is possible that the tag is in a non-optimal orientation towards the detection antenna. This may result in a miscommunication between the tag and the reader resulting in an unreliable timing or registration of the participant when crossing the detection antenna.
An example of a sporting event where both problems are particularly present is a triathlon event. Triathlon, in its most popular form, involves swimming, cycling, and running in immediate succession over various distances. Triathletes compete for fastest overall course completion time, including timed “transitions” between the individual swim, cycle, and run components. Triathletes may wear a sport timing tag somewhere on the body, e.g. on the chest, around the ankle or around the wrist, for accurate time registrations at detection points.
To be able to read the small backscattered signal generated by a sports timing tag, the detection antenna may be optimized for reading weak signals. For example, EP2009595 A1 discloses a solution for increasing the detectability of sport timing tags using antenna mats that are arranged in parallel with the finish line. EP2009595 A1 suggests reducing the number of misses (i.e. tags that cross the finish but are not detected by the antenna) by optimizing the radiation field of the antenna mats so that a homogenous interrogating and detection electromagnetic (EM) field over the whole finish line is generated. This solution however does not solve the problem of misses due to misorientation between the tag and the detection mat. Even when generating a homogenous EM field, the backscatter signal may be very weak due to the misorientation. Furthermore, implementation of the improved antenna mats in an existing timing system would require replacement of the mats, thereby rendering the non-optimized (legacy) detection antennas obsolete, which is not desirable in terms of costs and environmental issues.
Consequently, from the above it follows that there is a need in the art for cost efficient solutions to the above-identified problems associated with sports timing tags. In particular, there is a need in the art for a sports timing tag assembly that can be reliably used during sports events, including triathlon or similar events, on the basis of a legacy detection antenna.